The invention relates to data recording, and more particularly to control of recording power when recording information to alternating land/groove tracks on an optical disc.
In conventional phase-change optical discs, data is typically recorded on groove tracks. When data is recorded on groove tracks, land tracks guide laser beams and reduce crosstalk from adjacent groove tracks.
If data is recorded on both groove tracks and land tracks, density of data tracks may be doubled provided that the widths of the groove and land tracks are unchanged. Crosstalk between adjacent land and groove tracks may be reduced if the height differences between the land and groove tracks is ⅙ λ (wavelength of light source). Therefore, using both groove and land tracks is feasible to attain higher recording density. Accordingly, optical discs utilizing land/groove configuration such as DVD-RAM (digital versatile disc-random access memory) are developed, as well as opto-magnetic recording media such as ASMO (Advanced Storage Magneto-Optical) discs.
FIG. 1 illustrates configuration of a conventional optical disc comprising alternating land and groove tracks. As illustrated, the optical disk 10 is of a single-spiral configuration, in which groove track 11 and land track 13 are switched at header 151, and groove track 11 and land track 13 alternate along a single continuous spiral track. Each of the tracks is divided into a plurality of sectors 153 by the header 151 at the switch point and header 152 elsewhere in each revolution. In the illustrated example, there are 8 sectors per revolution, while in an actual design of an optical disc, there may be tens of sectors per revolution, and the number of sectors increases in the outer annular area.
FIG. 2 is a cross section of the described optical discs. Optical disc 20 comprises a plurality of alternating land tracks 22 and groove tracks 24. According to a conventional land/groove recording method, the same power level is used for recording data on the land and groove tracks, assuming that recording condition is the same for the land and groove tracks. Owing to the structural differences, however, the land and groove tracks have different recording conditions. Therefore, when recording on the land and groove tracks, a light beam of the same power may generate recording marks of different lengths on the land and groove tracks, respectively. As a result, bit error rate on groove and/or land track may increase. When recording information on both the land and groove tracks, recording power changes when recording track switches from a land track to a groove track, and vise versa.
According to a conventional method, when recording, intensity of light beams differs on land tracks and groove tracks. Type of data track is determined using information recorded on header field accompanied with each sector. For example, physical ID (PID) within the header field may be used to determine whether the data track is a land or groove track. Additionally, the data track type may be determined using signals obtained from a preamplifier. These conventional methods, however, are error-prone, especially under situations of high noise or high rotation speed.